1. Field of the Invention
The present invention relates generally to a self testing fault interrupting device, such as a ground fault circuit interrupter (GFCI). More particularly, the present invention relates to a self testing fault interrupting device where a periodic self test is performed on the fault detection and tripping portions of the device independent of a manual test.
2. Background of the Invention
Fault interrupting devices are designed to trip in response to the detection of a fault condition at an AC load. The fault condition can result when a person comes into contact with the hot side of the AC load and an earth ground, a situation which can result in serious injury. A ground fault circuit interrupter (GFCI) detects this condition by using a sense transformer to detect an imbalance between the currents flowing in the line and neutral conductors of the AC supply, as will occur when some of the current on the load hot side is being diverted to ground. When such an imbalance is detected, a relay or circuit breaker within the GFCI device is immediately tripped to an open condition, thereby removing all power from the load.
Many types of GFCI devices are capable of being tripped not only by contact between the line side of the AC load and ground, but also by a connection between the neutral side of the AC load and ground. The latter type of connection, which may result from a defective load or from improper wiring, is potentially dangerous because it can prevent a conventional GFCI device from tripping at the required threshold level of differential current when a line-to-ground fault occurs.
Prior art self testing fault protection devices typically provide a self test which replaces a user having to perform manual tests at fixed periods of time, for example, weekly, monthly, and so on. However, the self test involves the opening and closing of the GFCI's contacts. This can create a problem when sensitive equipment such as medical equipment is connected to the GFCI. The medical equipment cannot tolerate interruptions of a prolonged duration.
In addition, frequent testing is often necessary to insure the integrity of the GFCI. However, frequent testing often compounds the problem by increasing interruptions to sensitive equipment that is connected to the GFCI.
The performance of a manual test is an option on some GFCI protection devices. The user is required to press a test button which simulates a ground fault condition in GFCI protection devices resulting in the contacts of the GFCI protection devices opening. However, users usually forget or simply choose to ignore performing the manual tests.
An additional problem is that if the GFCI has a high cost, end users may select a lower cost GFCI that has the above mentioned problems without fully being aware of the disadvantages of the GFCI.
Therefore, a need exists for a self testing GFCI that is capable of providing periodic testing without interrupting the power supply to equipment that is connected to the GFCI. In addition, the GFCI device should preferably be low cost.